It is known that hydrocarbon propellants are used in certain formulations for aerosols. The hydrocarbons most commonly used for that purpose are: propane, n-butane and isobutane gases. These gaseous hydrocarbons are used alone as well as in various admixtures with each other or with low-boiling liquid hydrocarbons, in particular, pentane and isopentanes.
For instance, propane, in view of its too high vapor pressure, is commonly used together with other hydrocarbons with a higher boiling point, such as for instance n-butane, pentane and isopentanes. The hydrocarbons with an intermediate boiling point, such as isobutane, on the contrary, may be used alone by themselves.
The hydrocarbon propellants suffer from two serious drawbacks, as far as their use in aerosol compositions is concerned. The first drawback is their high inflammability. The second one consists in their low solvent power. In fact, they are not capable in general to form a homogeneous liquid phase with the other components of the formulations for aerosols, that is, the active principles, the solvents of said active principles and the various auxiliary ingredients habitually used. In certain cases it would be possible to obtain a homogeneous liquid phase containing the active principles if there were added high quantities of solvents, such as, for instance, ethanol or isopropanol; however, the formulations thus obtained would not contain a sufficient quantity of propellant in order to insure a correct and complete delivery of the formulation contained in the spraying bottles. Said formulations would likewise be very inflammable.
The hydrocarbon propellants are thus used almost exclusively in formulations containing an aqueous phase which contains the active principles in an emulsified or suspended state. During the use of the aerosol bombs, the presence of water in the aerosol jet reduces the risk due to the inflammability of the hydrocarbons. In the case of damages to the container, for instance, due to wear or corrosion, the propellant may, however, be delivered into the atmosphere with a consequential danger of explosion and fire. The possibility of such leakages of propellant makes the storing of the aerosol bombs rather unsafe, considering the possibility of an accumulation of hydrocarbon vapor in the storehouses.